Wildcard character

[Pawan Arora]

I don't understand, why the following block of code giving the compile time error:

public <T> List<T> meth(List<?> type)
{
System.out.println(type);
return new ArrayList<String>();
 
}

T means anytype, so why despite of passing the argument like

ArrayList<String> a=new ArrayList<String>, 

it's still giving the compile time error?

[Ove Lindström]

Originally posted by Pawan Arora:
I don't understand, why the following block of code giving the compile time error:

public <T> List<T> meth(List<?> type)
{
System.out.println(type);
return new ArrayList<String>();
 
}

T means anytype, so why despite of passing the argument like

ArrayList<String> a=new ArrayList<String>, 

it's still giving the compile time error?

No, T is just a template variable. [And you are using it twice as return value...]<-- This was wrong. You CAN declare it like that and then it will take the T from the parameter sent into it...

If I was to create a class of the type that the method resigns in using a String as T the generated method would look like this:

public List<String> meth(List<<String>> type)
{
System.out.println(type);
return new ArrayList<String>();
 
}

That is okey.

If I use an Integer, the code would translate to:

public List<Integer> meth(List<Integer> type)
{
System.out.println(type);
return new ArrayList<String>();
 
}

UPPS!! You can't return a List of Strings when I want you to return a list of Integers.

[ October 16, 2008: Message edited by: Ove Lindstr�m ]
[ October 16, 2008: Message edited by: Ove Lindstr�m ]

[Rob Spoor]

You either want to return an ArrayList<T>, or change the method signature to remove T and just return List<String>.